The present invention relates to a method for forming a gas cluster, ionization thereof, and a method for forming a thin film with this ion beam. More particularly, the present invention relates to a method for forming a thin film based on a gas cluster ion, which is a group of reactive substances liquid or gaseous at the room temperature, which is useful for manufacturing semiconductors and other electronic devices and for surface modification of functional materials.
Methods of modifying a surface or forming a thin film on a substrate surface by irradiating monatomic or monomolecular ions onto a substrate surface have conventionally been used in practice. Since it is difficult to obtain a beam having a practically sufficient density because of the space charge effect between ions with a low-energy ion irradiation in these methods, it is the usual practice to use a high incident energy of several keV.
However, in these conventional methods using ions having a high incident energy, it is difficult to avoid damages to the substrate surface to be treated, and deterioration of the substrate surface and thin film properties.
Conventionally available methods for depositing a thin film on a semiconductor substrate have included the vacuum CVD method and the plasma CVD method. The vacuum CVD method has however a problem in that a sufficient deposition rate cannot be obtained unless the substrate temperature is raised to over 400xc2x0 C. Consequently, when depositing a thin film such as lead titanate zirconate (Pb(Zr, Ti)O3) directly onto a silicon substrate, for example, Pb, Ti and Zr diffuse throughout the silicon substrate, resulting in deterioration of electric characteristics.
The plasma CVD method, known as a method for forming a thin film at a low temperature, is defective in that much impurities are mixed up, and ions damage the substrate surface, with difficulty of film thickness control of a produced extra-thin film, resulting in the impossibility to apply for an insulating film or a ferroelectric film requiring a high quality.
It has thus been difficult to obtain a high-grade ultra-thin film because the quality of a thin film has deteriorated according as the forming temperature of thin film has become lower in the conventional techniques.
Under these circumstances as described above, there has been a strong demand for development of a novel method permitting surface modification of a substrate and formation of a high-quality thin film at a lower temperature, or particularly at the room temperature without heating the substrate, as a basic technique directed toward progress of a more sophisticated electronics such as ULSI.
In this situation of technology, the present inventors have already proposed a method of forming a lumpy group of atoms or molecules from a gas-reactive substance gaseous at the room temperature under the atmospheric pressure and irradiating gas cluster ions generated by ionizing same onto a substrate surface.
This method permits cleaning and flattening of a substrate surface, as well as even formation of a thin film with a lower energy, and is therefore attracting the general attention as a technique for ultra-high-accuracy fine surface fabrication with the use of a low-energy beam hereafter.
In spite of the considerable potentiality of this cluster ion beam, however, the technique has just paved the way to development, and many problems are still left for future resolution, including, for example, restriction on the kind of gas component substances and applications thereof.
The present invention was developed in view of the circumstances as described above, and has an object to provide a novel method related with gas cluster ion beam, which permits formation of a high-quality thin film having a flat and smooth interface in a state free from damage to the substrate at a relatively low temperature, through further development of the gas cluster beam technique.
As means to solve the above-mentioned problems, the present invention provides a method for forming a gas cluster, which comprises the steps of mixing a substance liquid at the room temperature under the atmospheric pressure and a pressurized gas, and causing the resultant mixture to spout as a gas from a nozzle to generate a cluster which is a lumpy group of atoms or molecules (claims 1 to 6).
The present invention provides also a method for forming gas cluster ions, which comprises the step of ionizing the thus formed gas cluster (claims 7-8), and a method for forming a thin film, which comprises the step of irradiating the thus formed cluster ions onto a substrate surface, thereby forming a thin film (claims 9-10).
Furthermore, the present invention provides a method for forming a thin film, which comprises the steps of forming a cluster which is a lumpy group of atoms or molecules of a reactive substance gaseous at the room temperature, irradiating cluster ions ionized therefrom onto a substrate surface, and at the same time or alternately, irradiating a single, or a plurality of, component gas of a deposit film onto the substrate surface to cause reaction of the both, thereby depositing a thin film on the substrate surface (claims 11-14), a method for forming an oxygen-containing gas cluster, which comprises the step of causing an oxygen-containing pressurized gas mixed with a rare gas to spout from a nozzle to form a gas cluster (claims 15-16), a method for forming an oxygen-containing gas cluster ion resulting from ionization thereof (claim 17), and a method for forming a thin film, which comprises the step of irradiating this ion onto a substrate surface, thereby forming a thin film (claim 18).